Pistachios grow on trees in grape-like clusters and are encased in an outer skin, or hull. When pistachios ripen, the hull turns rosy and the shell within splits naturally, indicating they are ready for harvest, usually in September. Pistachios are mechanically shaken from the trees onto a catching frame, never touching the ground. Each tree takes less than a minute. They are loaded onto containers and rushed to the processing plant where hulling, drying and sorting are completed. Later the nuts are roasted, salted and sometimes dyed. If the nuts are not processed [hulled and dried] within 12 to 24 hours, the shell will be stained. The pistachio industry has invested millions of dollars in equipment to process its pistachios quickly to avoid staining and sell the nuts in their natural color shells. Some pistachio processors dye a small percentage of their pistachios not by necessity, but to meet the desires of those consumers who prefer colorful shells.